PVS-Studio warning V610 for Chromium

bool WebMClusterParser::ParseBlock(....)
{
  int timecode = buf[1] << 8 | buf[2];
  ....
  if (timecode & 0x8000)
    timecode |= (-1 << 16);
  ....
}

This suspicious code was found in Chromium project by PVS-Studio static code analyzer.
Warning message is:
V610 Undefined behavior. Check the shift operator '<<. The left operand '-1' is negative. webm_cluster_parser.cc 217

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/